Valve control device for an internal combustion engine

ABSTRACT

A valve control device for an internal combustion engine having a gas exchange valve for controlling an inlet and/or outlet cross section in the combustion chamber of the engine. The valve control device has an axially movable gas exchange valve member whose valve member shaft is coupled to a piston rod to a differential piston that can be hydraulically actuated. The differential piston is embodied as two piston parts, wherein the two piston parts are disposed in relation to one another in such a way that they are operatively connected to each other in the axial direction and can execute a radial relative movement in relation to each other.

PRIOR ART

The invention is based on a valve control device for an internalcombustion engine. In a valve control device of this kind, which hasbeen disclosed by DE 195 11 320 A1, a piston-shaped valve member of agas exchange valve controls the opening and closing of an inlet andoutlet cross section on the combustion chamber of the engine to be fed.The gas exchange valve, which is embodied as a disk valve, has anaxially movable valve member whose valve member shaft is coupled by wayof a piston rod to an adjusting piston (differential piston) that can behydraulically actuated, by which the individual gas exchange valve canbe directly actuated independently of the other gas exchange valves. Thehydraulic adjusting piston in the known valve control device is therebydisposed directly on the valve member shaft or the piston rod of the gasexchange valve and thereby constitutes a part of the gas exchange valvemember itself. With a lower annular end face, the adjusting pistondefines a first hydraulic working chamber and with its upper piston endface, defines a second hydraulic working chamber, and these workingchambers can be filled with a highly pressurized pressure fluid andemptied by way of corresponding pressure fluid lines. The hydraulicworking pressure in the lower working chamber acts on the adjustingpiston in the closing direction of the gas exchange valve and the upperworking chamber acts on the adjusting piston in the opening direction ofthe valve member of the gas exchange valve. It is then possible, throughthe alternating filling of the working chambers with high pressure, tohydraulically actuate the adjusting piston and to thus move the valvemember of the gas exchange valve rigidly connected to it in the openingor closing direction.

The known valve control device, however, has the disadvantage that astatic redundancy occurs on the adjusting piston, which is caused by adouble centering of the adjusting piston. Since the hydraulic adjustingpiston is guided directly on its outer circumference surface and is alsoguided on its inner surface by way of the piston rod firmly connected tothe adjusting piston, along a second guide surface of the valve member,which even with extremely small tolerance deviations can cause thehydraulic adjusting piston to stick and can result in a jamming of thegas exchange valve.

Valve control devices have also been disclosed in which the hydraulicadjusting piston is fastened to the valve member shaft of the gasexchange valve by means of a screw thread. This has the furtherdisadvantage that the transmission of force from the hydraulic adjustingpiston to the valve member shaft occurs by way of the screw thread,which results in a high dynamic alternating tension/pressure stress in azone with a concentration of stress, which can cause fatigue fracturesthere.

ADVANTAGES OF THE INVENTION

The valve control device has the advantage over the prior art that thehydraulic differential piston actuating the gas exchange valve has aradial play between its two guide surfaces, or in relation to the guidesurface of the gas exchange valve.

This is achieved in a structurally advantageous manner by virtue of thefact that the piston of a hydraulic valve actuation device, which ispreferably embodied as a differential piston, has two parts, wherein thetwo piston parts are guided so that they can slide axially, areoperatively connected to each other, and have a radial play in relationto each other. Consequently, the two piston parts can execute a relativemotion in the radial direction in relation to each other, which in theevent of tolerance deviations, reliably prevents a jamming of thedifferential piston and thus reduces the manufacturing costs with regardto tolerance sensitivity. In order to nevertheless assure a reliablesealing of the two hydraulic working chambers defined by thedifferential piston, the two-part differential piston is embodied sothat a first piston part slides in a sealed fashion with a largediameter on its radial outer circumference surface against a cylinderguide surface, wherein it has a radial play in relation to the pistonrod of the gas exchange valve that passes through it axially. Thesecond, smaller diameter piston part is guided in a sealed fashion withits radial inner wall surface against the piston rod and has a radialplay in relation to the cylinder guide wall. The two piston parts cannow move radially in relation to each other during operation, whereinthe axial piston end faces that are oriented toward each other restagainst each other in a sealed fashion. Alternatively, however, it isalso possible to provide an axial sealing element, e.g. a sealing disk,between the end faces of the piston parts of the differential piston.Furthermore, it is possible to embody one of the two piston end faces asball-shaped in order to produce a reliable seal between the end faces.

The two piston parts are also operatively connected to the piston rod inthe axial direction by way of axial stop faces and have a slight axialplay that permits a radial compensation movement in relation to eachother. The valve member shaft of the gas exchange valve isadvantageously embodied as being of one piece with the piston rod of thedifferential piston and is advantageously guided axially in a guide bushwhose end wall surface simultaneously defines a lower hydraulic workingchamber. On the one end, the stop face on the piston rod isadvantageously embodied as an annular stop face which comes into directcontact with the one end face of the differential piston. The secondstop is advantageously constituted by a separate component, which ispress-fitted onto the shaft of the piston rod, is embodied as a valvewedge, and can be placed around the piston rod as a result of having amulti-part form.

On its outer circumference, this wedge-shaped component has a conicalcross sectional expansion in the direction of the differential pistonand a corresponding cone ring is slid axially against this expansion.The clamping force directed radially inward is exerted by means of aclamping nut that is screwed onto the piston rod and thereby clamps thecone ring through the radial clamping of the wedge-shaped stopcomponents. A lower end face of the wedge-shaped stop components thusconstitutes a stop face, which cooperates with an upper annular end faceof the differential piston. In order to define the position of thewedge-shaped stop components on the shaft of the piston rod, it is alsoadvantageous to provide the valve wedges with ribs that protruderadially inward and engage in a corresponding groove on the shaft of thepiston rod.

In order to prevent a loss of the clamping force exerted by the clampingnut, and in order to also permit an axial compensation of play, it isalso advantageous to provide a spring element between the nut and thecone ring, which spring element is preferably embodied as a spring diskor spring ring and can have a U-shaped contour.

With the above-described disposition and fastening of the upper stop tothe piston rod, it is possible to guide the larger diameter differentialpiston part with radial play in relation to the shaft of the piston rodand in a sealed fashion inside the cylinder housing and to guide thesmaller diameter differential piston part with radial play in relationto the cylinder housing wall and in a sealed fashion against the pistonrod, wherein the working chambers axially adjoining the differentialpiston are completely sealed off from one another by the axial sealbetween the differential piston parts. Consequently, the two pistonparts of the differential piston can be axially guided independently ofone another against the guide surfaces, with very tight fits ortolerances. As a result, the elastic sealing elements required in knownvalve control devices are no longer necessary.

Alternatively, it is also possible to replace the piston rod completelyby means of the valve member shaft of the gas exchange valve.

Furthermore, the currently separate guidance of the individual pistonparts permits high relative speeds of the individual sealing surfaces onthese components in relation to one another. Because of the radial playbetween the piston parts, it is also possible for there still to be areliable transmission of force in both axial directions even at hightemperatures, wherein no dynamic loads are introduced onto the thread ofthe clamping nut of the upper stop.

It is consequently possible with the valve control device according tothe invention to integrate the gas exchange valve member shaft into theactuator of a hydraulic valve actuator and thereby to fasten the valvemember shaft directly to the hydraulic differential piston withoutradial forces or moments being transmitted between these two movingcomponents.

In this connection, the invention is described in conjunction with avalve control device in which both the opening and closing motion of thegas exchange valve member are executed hydraulically; alternatively,however, it is also possible to execute the closing stroke motion ofvalve member of the gas exchange valve mechanically, e.g. by means of avalve spring.

Furthermore, in the above-described exemplary embodiment, the hydraulicpiston is directly connected to a piston rod that is embodied of onepiece with the valve member shaft of the gas exchange valve.Alternatively, however, it is also possible to fasten the hydraulicpiston to a piston rod which is in turn coupled to the valve membershaft of the gas exchange valve outside the cylinder.

It is also possible to embody the differential piston part which isguided against the piston rod in a sealed fashion as being of one piecewith the piston rod or to press-fit this piston part onto the pistonrod.

Other advantages and advantageous embodiments of the subject of theinvention can be inferred from the following description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the valve control device according to theinvention for an internal combustion engine is shown in the drawing andwill be explained in detail below.

The sole FIGURE shows a longitudinal section through the valve controldevice as well as the lower end of the gas exchange valve member withthe valve disk and the corresponding valve seat on the combustionchamber of the engine to be fed.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The valve control device for an internal combustion engine is shown in asimplified sectional representation in the sole FIGURE. The valvecontrol device has a gas exchange valve 1 whose piston-shaped gasexchange valve member 3 can move axially. A valve sealing face 5 on adisk-shaped valve member head 7, cooperates with a stationary valve seat9 on the housing 11 of the engine in order to control an inlet or outletcross section 13 of the combustion chamber of the engine. The gasexchange valve member 3 has a valve member shaft 15 which transitionsinto a piston rod 16 that is of one piece and protrudes into a cylinderhousing 17 of a hydraulic adjusting device. The piston rod 16 has acylindrical, two-part differential piston 18 disposed on it, with afirst, larger diameter piston part 19 whose axial through opening wall21 has a radial play 20 in relation to the piston rod 16. The largerdiameter differential piston part 19 is guided with an outercircumference wall surface resting against a guide wall surface 22 inthe cylinder housing 17 in a sealed, sliding fashion, and with axial endfaces, respectively defines hydraulic working chambers in the cylinderhousing 17. A lower end face 23 of the piston part 19 that is close tothe combustion chamber defines a lower hydraulic working chamber 25,which can continue into the radial, annular gap 20 via a play betweenthe piston rod 16 and the piston part 19.

A second piston part 51 of the differential piston 18 is embodied with asmaller diameter than the first piston part 19. This piston part 51 isguided in a sealed fashion against the shaft of the piston rod 16 andhas a radial play in relation to the guide wall 22 of the cylinderhousing 17. The piston parts 19, 51, with their axial end faces orientedtoward one another, rest in a sealed fashion against one another,wherein a radial relative movement of the piston parts 19, 51 inrelation to one another is possible. With its end face 27 remote fromthe gas exchange valve 1, the differential piston 18 defines another,upper hydraulic working chamber 29 in the cylinder housing 17.

The working chambers 25 and 27 can be filled with a hydraulic workingmedium and emptied by way of pressure fluid lines 31, 33, wherein in theexemplary embodiment described above, the openings of the pressure fluidlines can each be opened and closed in a manner that is not shown indetail by means of a respective control valve, preferably a solenoidvalve, as a function of a control unit.

At its entry into the cylinder housing 17, the valve member shaft 15 orthe piston rod 16 is axially guided in a sealed fashion by means of aguide sleeve 35. The guide sleeve 35, which is inserted in a sealedfashion with its outer circumference into the cylinder housing 17defines the lower working chamber 25 on its end remote from thedifferential piston 18 with its upper end wall face 37 protruding intothe cylinder housing 17. The upper working chamber 29 is closed on itsend remote from the differential piston 18 by means of an end wall ofthe cylinder housing 17.

On its circumference surface, the piston rod 16 has two stops which canbe contacted by the end faces 23, 27 of the differential piston 18 inboth axial adjustment directions.

In this connection, a lower shoulder 39 constitutes a first stop face onthe piston rod 16, wherein the shoulder 39 is formed by a crosssectional reduction of the shaft of the piston rod 16 in the directionof the end remote from the combustion chamber. However, the largerdiameter differential piston part 19 rests with its lower piston endface 23 against this shoulder 39 only when there is no high pressureprevailing in the lower working chamber 25. Otherwise, the high pressurein the lower working chamber 25 holds the piston part 19 in contact withthe upper stop so that between the shoulder face 39 on the piston rod 16and the lower piston end face 23 on the piston part 19, a slight axialplay remains, by means of which the pressure fluid can flow into theannular gap 20 and by means of which the piston rod 16 and thedifferential piston 18 can move axially in relation to each other. Thisplay is necessary in order to prevent a static redundancy of the systemsince the closing stroke motion of the gas exchange valve member 3 islimited by the centering action during the contact with the valve seatface 9.

On the upper end of the piston rod 16 that is remote from the combustionchamber and protrudes from the differential piston 18, a valve wedge 41comprising two shells is disposed on the shaft of the piston rod 16.This wedge 41 is embodied as annular and rest with cylindrical innerwall faces flush against the piston rod shaft 16. The outer wall facesof these wedges are embodied conically, wherein the wall thickness ofthe wedges 41 increases uniformly in the direction toward thedifferential piston 18. Furthermore, the wedges 41, on their inner wallfaces, have an annular rib 43 which protrudes into a correspondingannular groove 45 in the circumference wall of the piston rod 16. Thisobliquely extending radial outer circumference wall of the wedges 41 hasa cone ring 47 slid axially onto the wedges 41 whose inner wall diameterconically decreases in the direction toward the differential piston 18in a fashion complementary to the cone angle of the wedges 41. The conering 47 is pressed axially against the wedges 41 by means of a clampingnut 49, for which purpose the clamping nut 49 is screwed onto a thread53 provided on the upper end of the piston rod 16.

As a result, the wedges 41 are clamped radially against the shaft of thepiston rod 16 so that the transmission of force from the differentialpiston 18 onto the piston rod 16 and furthermore onto the shaft 15 ofthe gas exchange valve member 3 takes place by way of the wedges 41 andthe thread 53 is not exposed to any changing stresses related to theintroduction of force.

Through the alternative interposition of a spring ring, not shown indetail, between the cone ring 47 and the clamping nut 49, settlingphenomena of the components can be compensated for and the necessaryinitial stress in the axial connection can be maintained.

In this connection, the lower annular end face of the wedges 41 orientedtoward the differential piston 18 constitute the second stop face on thepiston rod 16 in which the second piston part 51 of the differentialpiston 18 comes into contact.

The seal between the upper working chamber 29 and the lower workingchamber 25 thereby takes place by means of the radial inner wall surfaceof the smaller piston part 51, which is disposed in a sealed fashionagainst the piston rod 16, the sealed contact between the end faces ofthe piston parts 51, 19, and the radial outer wall guidance between thelarger piston part 19 and the guide wall 22 of the cylinder housing 17.

In order to seal the lower working chamber 25 in relation to theoutside, a sealing ring can also be provided between the guide sleeve 35and the shaft of the piston rod 16 in order to thus permit a playbetween the piston rod 16 and the guide sleeve 35.

The axial guidance of the piston rod 16 and the differential piston 18or the valve member shaft 15 is thereby executed merely by means of thecircumference surfaces of the piston rod 16 and the differential pistonpart 19, wherein the two piston parts 51 and 19 of the differentialpiston 18 can thereby execute a relative motion in the radial directionin relation to one another, which reliably prevents a tilting andjamming of the differential piston 18 in the cylinder housing 17 even inthe event of tolerance deviations.

The valve control device according to the invention for an internalcombustion engine functions in the following manner. When at rest, i.e.when the valve member 3 is resting against the valve seat 9, thehydraulic pressure in the lower working chamber 25 exceeds the hydraulicworking pressure in the upper working chamber 29 so that thedifferential piston 18 is acted on in the direction of the upper workingchamber 29 and thus, the gas exchange valve member 3 is fixed in itsclosed position. If an opening event of the gas exchange valve 1 shouldnow be produced, the lower working chamber 25 is depressurized (oralternatively brought to the same pressure level) via of the controlvalve, not shown in detail, and the pressure fluid line 31 and at thesame time, the upper working chamber 29 is filled with a highlypressurized pressure fluid by means of the pressure fluid line 33 sothat the adjusting force acting on the differential piston 18 in theupper working chamber 29 exceeds the adjusting force acting on thedifferential piston 18 in the lower working chamber 25 since the totalpressure engagement area of the differential piston 18 is greater in theupper working chamber 29 and in the lower working chamber 25. As aresult, the high pressure prevailing in the upper working chamber 29moves the differential piston 18 in the direction of the lower workingchamber 25, wherein the gas exchange valve member 3, 15, which isconnected to the differential piston 18 by way of the piston rod 16, ismoved in the direction of the combustion chamber. As a result, with itsvalve sealing face 5, the valve member 3 lifts away from the valve seat9 and clears an inlet or outlet cross section 13 from a supply conduitinto the combustion chamber of the engine, which is not shown in detail.

The closing stroke motion of the valve member 3 takes place again bymeans of a depressurization of the upper working chamber 29 and apressurization of the lower working chamber 25, as a result of which thedifferential piston 18 and along with it, the gas exchange valve member3 are moved in the direction of the upper working chamber 29 again untilthe valve member 3, with its valve sealing face 5, rests once more in asealed fashion against the valve seat 9. The reciprocal filling anddischarging of the working chambers 25 and 29 takes place by way ofsolenoid valves in the pressure fluid lines 31, 33 which are controlledas a function of operating parameters of the engine by way of a controlunit that is not shown in detail.

The foregoing relates to a preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A valve control device for an internal combustionengine comprising a gas exchange valve (1) for controlling an inletand/or outlet cross section (13) on a combustion chamber of the engine,the gas exchange valve has an axially movable gas exchange valve member(3) with a valve member shaft (15) which is coupled to a piston rod(16), the gas exchange valve is embodied as one piece with the gasexchange valve member shaft (15), coupled to a differential piston (18)that is hydraulically actuated in a cylindrical housing (17), thedifferential piston (18) is embodied as two parts wherein the twodifferential piston parts are disposed in relation to one another insuch a way that the two differential piston parts are operativelyconnected to each other in an axial direction and can execute a radialrelative movement in relation to each other.
 2. The valve control deviceaccording to claim 1, in which said differential piston (18) includes alarger diameter piston part (19), with a radial outer circumferencesurface that constitutes a first guide surface of the differentialpiston (18), said differential piston (18) is guided so that it canslide in a sealed fashion against a guide wall (22) of the cylinderhousing (17), and that another, smaller diameter piston part (51), witha radial inner wall surface, constitutes a second guide surface of thedifferential piston (18), which is guided in a sealed fashion againstthe piston rod (16), wherein the two larger and smaller piston parts(19, 51) can execute a radial relative motion in relation to each other.3. The valve control device according to claim 2, in which the largerand smaller piston parts (19, 51), with their end faces oriented towardeach other, rest against each other in a sealed fashion.
 4. The valvecontrol device according to claim 2, in which the larger diameter pistonpart (19) has a radial play (20) in relation to the piston rod (16) thatpasses through the larger diameter piston part and the smaller diameterpiston part (51) has a radial play in relation to the guide wall (22).5. The valve control device according to claim 1, in which thedifferential piston (18) defines two hydraulic working chambers in saidcylinder housing (17), each of which can be filled with a pressure fluidand emptied by way of separate pressure fluid lines.
 6. The valvecontrol device according to claim 5, in which a lower end face (23) ofthe larger diameter differential piston part (19), which is close to thecombustion chamber, defines a lower working chamber (25) whose hydraulicinternal pressure acts on the differential piston (18) in the closingdirection of the gas exchange valve member (3).
 7. The valve controldevice according to claim 5, in which an upper end face (27) of thedifferential piston (18), which is remote from the combustion chamber,defines an upper working chamber (29) whose hydraulic internal pressureacts on the differential piston (18) in the opening direction of the gasexchange valve member (3).
 8. The valve control device according toclaim 2, in which a shoulder (39) is provided on the piston rod (16),said shoulder (39) cooperates with a lower end face (23) of the largerdiameter differential piston part (19) disposed close to the combustionchamber.
 9. The valve control device according to claim 2, in which onan end of said piston rod that is remote from the combustion chamber andwhich protrudes from the differential piston (18), the piston rod (16)has a stop (41) with a stop face which cooperates with an upper end face(27) of the differential piston (18) remote from the combustion chamber,wherein the stop (41) is provided on a component that is press-fittedonto the piston rod (16).
 10. The valve control device according toclaim 9, in which the component which constitutes the stop is composedof at least one wedge (41), which at least partially encompasses thepiston rod (16) and whose inner wall surface that is directed radiallyinward rests against the piston shaft (16) and whose outer wall surfacethat is directed radially outward extends conically in such a way that awall diameter of the wedge (41) increases in a direction toward thelarger differential piston part (19).
 11. The valve control deviceaccording to claim 10, in which two shell-shaped wedges (41) areprovided which, on their outer circumference wall, are radiallyencompassed by a cone ring (47), an internal cross-section of the conering decreases conically in a direction of the larger differentialpiston part (19) in a fashion complementary to a cone angle of thewedges (41) and which is axially clamped against the wedges (41) bymeans of a clamping nut (49) that is screw threaded onto an end of thepiston shaft (16).
 12. The valve control device according to claim 10,in which ribs (43) protruding radially inward on the inner wall surfacesof the wedges (41) engage in corresponding grooves (45) in the pistonshaft (16).
 13. The valve control device according to claim 10, in whichthe stop face is formed on the lower end face of the wedges (41)oriented toward the larger diameter differential piston part (19). 14.The valve control device according to claim 6, in which the lowerworking chamber (25) disposed close to the combustion chamber, on an endremote from the differential piston (18), is defined by a guide sleeve(35) and the piston rod (16) protrudes outward through said guidesleeve.